What is more important? Speed V Pellet V Barrel

[Vetmx]

I don't think the pellet seating depth is a large factor but it wouldn't be too hard to make a simple tool to push the pellet further into the barrel if you wanted to test the effect. On a PB the distance from the point of the bullet that will contact the rifling and the rifling changes the pressure build up. The peak pressure is lower if you let the bullet jump a little to the rifling. Chambering the bullet hard into the rifling will increase pressure. But in an airgun we are not burning anything (hopefully) so we cannot affect powder combustion. I guess you could theorize that pushing the pellet firmly into the rifling would allow pressure to build a little more in the "chamber" possibly increasing velocity a little. Anything like this could affect the harmonics and thus accuracy but my guess is the sliding of the pellet down the barrel is a much bigger driving force for the harmonics.

If you want to test my theory that your leade is cut too deep and find out how important pellet depth actually is, just manually seat some 25.39’s in your gun that only likes 33.95’s. A ”L” shaped allen wrench can be used as your loading tool. Chamber one with your probe, then push on it with the allen wrench if you feel it pop in, prepare yourself for some good groups and a search to find someone to build you a new barrel.

 

[JimD]

I'm thinking of something similar to test the effect. I may try to adjust the pellet seating depth in small increments to see first if there is an effect and second, what depth works best. I won't change the barrel regardless but might modify the pellet probe. All my P35s are shooting pretty well - over 190 on the 30 yard challenge. So I don't expect to see much improvement. But your idea of trying some 25 grain that the gun doesn't care for is interesting. But I would think if the start of the rifling/seating depth would have made a bigger effect when I was shooting 20 grain at my old low power tune. They shot about the same as the 34 grain at the low power tune.

 

[Vetmx]

You are going to be limited on your seating depth because if you make a longer probe, it won’t clear your mag. I’ve been down the Chinese .25 road before. We are already derailing this interesting topic enough. Don’t fight it. Just see what your gun is probably capable of by seating some 25gr manually just a little further than your probe will.

 

[JungleShooter]

You are going to be limited on your seating depth because if you make a longer probe, it won’t clear your mag. I’ve been down the Chinese .25 road before. We are already derailing this interesting topic enough. Don’t fight it. Just see what your gun is probably capable of by seating some 25gr manually just a little further than your probe will.

Frank,

what you're saying is intriguing.

Wonder why so few people have suggested this technique in all those years that I've been reading forum posts....
I definitely need to do some testing!!

Matthias

 

[Vetmx]

Frank,

what you're saying is intriguing.

Wonder why so few people have suggested this technique in all those years that I've been reading forum posts....
I definitely need to do some testing!!

Matthias

You have a Prophet with some of the best barrels in the business. You do not need to waste one pellet or moment of your time testing this issue.

 

[JungleShooter]

You have a Prophet with some of the best barrels in the business. You do not need to waste one pellet or moment of your time testing.

You're so kind!


Yeah, sounds good — however — I still need to do the slug run —
seeing if I have anything on the shelf that will give me a 1 moa of pigeon lungs....


Can't help myself. It's that particular rabbit hole....

Matthias

 

[Vetmx]

You're so kind!


Yeah, sounds good — however — I still need to do the slug run —
seeing if I have anything on the shelf that will give me a 1 moa of pigeon lungs....


Can't help myself. It's that particular rabbit hole....

Matthias

Your seating depth is what it is unless you have a lathe and a pin reamer. So you will just have to work on size. You will need the combination for the lock on that door if you decide to open it. The combination is 249.

 

[JungleShooter]

Your seating depth is what it is unless you have a lathe and a pin reamer. So you will just have to work on size. You will need the combination for the lock on that door if you decide to open it. The combination is 249.

Thanks for being the safe cracker for me, Frank!

➧ That's a good way to start 2024.

➠ I hope you have a good start as well! Thanks for all your contributions you're making to so many of us.

Matthias

 

[lbc_PSI]

Not sure if it' OK to post to data on other forums, but I found this on skirt depth...

Pellet skirt depths and bearing lengths - Airguns & Guns Forum

Pellet skirt depths and bearing lengths, Air guns, Airgun Forum

www.gatewaytoairguns.org

Not sure if this matters..or it may already have been discussed somewhere..but..

Why are the interior of pellet skirts flat? Specifically, the bearing surface where the probe contacts to push the pellet. Like "H"

Maybe there are pellets that are non-flat...if so disregard this thought train.. But wouldn't a cone shape be better? Like "X"

If you try to balance a paper cup on it's flat bottom using a pencil (IE..turn it upside down and insert the pencil into the mouth of the cup) ..even if you're off center a little bit, the paper cup sits cock-eyed. Now if you were to balance a cone shaped paper cup (think snow cone) the pencil naturally seems to find the center of the cup.

It seems as though the flat bottom of pellet skirts could naturally induce a very slight off center bias..unless of course the probe contacts the inside of the skirt exactly in the center of the pellet skirt and doesn't apply any off axis pressure as the pellet is pushed from the magazine into the barrel.

The "X or "V" shape inside the pellet skirt would guide the probe to the exact center every time..allowing the probe to exert the same amount of pressure and self-centering the pellet as it is slid into the barrel.

Does that make any sense at all?

 

[tnt68]

Not sure if it' OK to post to data on other forums, but I found this on skirt depth...

Pellet skirt depths and bearing lengths - Airguns & Guns Forum

Pellet skirt depths and bearing lengths, Air guns, Airgun Forum

www.gatewaytoairguns.org

Not sure if this matters..or it may already have been discussed somewhere..but..

Why are the interior of pellet skirts flat? Specifically, the bearing surface where the probe contacts to push the pellet. Like "H"

Maybe there are pellets that are non-flat...if so disregard this thought train.. But wouldn't a cone shape be better? Like "X"

If you try to balance a paper cup on it's flat bottom using a pencil (IE..turn it upside down and insert the pencil into the mouth of the cup) ..even if you're off center a little bit, the paper cup sits cock-eyed. Now if you were to balance a cone shaped paper cup (think snow cone) the pencil naturally seems to find the center of the cup.

It seems as though the flat bottom of pellet skirts could naturally induce a very slight off center bias..unless of course the probe contacts the inside of the skirt exactly in the center of the pellet skirt and doesn't apply any off axis pressure as the pellet is pushed from the magazine into the barrel.

The "X or "V" shape inside the pellet skirt would guide the probe to the exact center every time..allowing the probe to exert the same amount of pressure and self-centering the pellet as it is slid into the barrel.

Does that make any sense at all?

More or less the probe and the skirt must match together but there is also the tranfer port in many barrels. I've made the pin a little bit rounded and then polished to accomplish the matching to the skirt but also polished the edges of the transfer port not to cut the skirt. My conclusion is that the barrel is the main thing to take care of. After the labour I've done my RTI .177 LW barrel sub 7.5Joule/5.5ft-lb(160-175ms/525-575fps) is better performing with a wider variety of pellets than before.

 

[JimD]

P35s do not use a pin probe to seat the pellets, they have a tube. So they push on the edge of the skirt rather than up inside of the skirt. I'm not sure what difference it makes relative to seating but I have noticed that some pellets seem more hollow than others. For a probe that pushes on the skirt it wouldn't matter but with a pin probe, if the pellet has a long opening the pellet will not be seated as deeply.

 

[JimD]

I got bored and did a little test today. I attached the target. These are all 5 shot groups at 30 yards with my P35-25. The two columns on the left are 34 grain pellets and the two on the right are 25.4 grain pellets. Mostly JSBs but in the top row, the two inboard targets are FXs. As you go down the target the seating depth of the pellet was increased. I used my Husky allen wrench set. The 1.5mm seemed to project about the depth the pellet probe seated the pellet. I measured it's projection at 13.58mm or .535 inch. The second row of targets was with the 2mm wrench which projects 15.78mm or .621 inches. The third row is supposed to be with the 2.5mm wrench but I messed up with the far right target in this row and used the 2mm again. So I shot the left target in that cell with the correct wrench. It is the smallest group. The last row has pellets seated with the 3mm wrench which I measured at 18.32mm or .721 inches. So the pellets were inserted into the barrel almost 0.2 inches further in the lowest targets than the top row with a couple intermediate steps.

My earlier conclusion that 34 grain shoot better than 25.4 grain in this gun is not supported by this target. The 25.4 grain groups are smaller. But the differences are not large. Since I retuned this gun it has been shooting 0.25 to 0.5 inch groups pretty consistently. These groups are basically within that range except for a few with the 34 grain seated deeper. There was some left to right wind as I was shooting. I'm sure that effected groups a little.

This is not a lot of data. It is only one gun and only a few groups. But I see no indication that seating the pellets further into the barrel reduces group size. I really like that one group with the JSB 25.39 pellets seated with the 2.5mm allen wrench. If I had more of those pellets I would try to duplicate it but I am pretty sure I cannot. I think it is just a little luckier than the other groups. I have a very similar group with the FX 34s.

I have a new SPA barrel for this gun on the way. I bought it before retuning it and it is shooting much better after the retune. But I am holding off stocking up on 25 caliber pellets until I see what that barrel is like. I could still standarize on 25.4s for this gun but will probably use 34s as long as the accuracy seems to be about the same. I want the greater penetration of the 34s in case another raccoon needs to be dispatched.

I was measuring velocity as I shot. The 25.4s were going 886 to 892.6 fps. The 34s velocity was 790.8 to 802.9. The lowest velocity was the first shot with the 34s, the 790.8. It was within 10 fps of the other JSBs, however. The highest velocity for the 34s was the FX. Most of the 5 shot groups varied around 5 fps between shots but the FX 34s were from 802.2 to 802.9. Less than 1 fps variation over 5 shots. Probably just another quirk in the data.

 

[HogKiller]

There is one more little thing that can take an absolutely perfect match of barrel and slug and turn it into a horrible mess. Too much air, I gleaned this little tidbit off of a video of Matt Gruber (sic??) If you have too much air behind the slug it'll cause wobble as it exits the muzzle and you will NEVER EVER get a consistent shot. This is the one tidbit of information that is absolutely vital as you get the right speed for the barrel to find that sweet spot for just enough air and not a lick more. You get your speed then slowly and I mean SLOWLY in tiny increments, start dialing back to where it falls off, up a tiny bit and you should be golden. www.youtube.com/watch?v=AxDXCDKO1S0 (11:43) He's setting up a M3 but....it applies to any gun. I do have a slight 'disagreement' about the need for slug probes and slug ports because I've found that using a slug probe, not a pin and the pellet port, let's me shoot my lighter 22gr (22.gr.) 500mm barrel or 26gr (.25 cal) 600mm barrel at the perfect speeds and my guns sip air. I refill because I'm getting bored and need something to do.

 

[Airgunmann]

If you want to test my theory that your leade is cut too deep and find out how important pellet depth actually is, just manually seat some 25.39’s in your gun that only likes 33.95’s. A ”L” shaped allen wrench can be used as your loading tool. Chamber one with your probe, then push on it with the allen wrench if you feel it pop in, prepare yourself for some good groups and a search to find someone to build you a new barrel.

On my pre airforce Raw there wasn't any leade cut into it which seemed to work great with pellets

 

[Vetmx]

On my pre airforce Raw there wasn't any leade cut into it which seemed to work great with pellets

Yes, Leshiy‘s have no leade and they shoot pellets great. None at all with no sharp edges is better than a deep leade where the pellet gets a running start then gets jacked up when it hits the rifling.

 

[JimD]

Hogkiller, your thoughts are interesting to me relative to my P35-177. I'm planning to retune it to see if I can improve the accuracy. I already have the hammer spring a little below the point of maximum velocity for the regulator setting but could turn it down a little more before turning the regulator down a little. It shoots pretty well (best 30 yard challenge target is a 194) but it seems like it could do better. I haven't changed the regulator setting since I got it. It shoots 10 grain JSB knockouts TERRIBLY while others report great accuracy with them in essentially the same gun. But something knocking them into instability would explain the way they shoot. I've polished the crown and the barrel so a tweak to the tune seems like the next step.

 

[JDGriz]

There is one more little thing that can take an absolutely perfect match of barrel and slug and turn it into a horrible mess. Too much air, I gleaned this little tidbit off of a video of Matt Gruber (sic??) If you have too much air behind the slug it'll cause wobble as it exits the muzzle and you will NEVER EVER get a consistent shot. This is the one tidbit of information that is absolutely vital as you get the right speed for the barrel to find that sweet spot for just enough air and not a lick more. You get your speed then slowly and I mean SLOWLY in tiny increments, start dialing back to where it falls off, up a tiny bit and you should be golden. www.youtube.com/watch?v=AxDXCDKO1S0 (11:43) He's setting up a M3 but....it applies to any gun. I do have a slight 'disagreement' about the need for slug probes and slug ports because I've found that using a slug probe, not a pin and the pellet port, let's me shoot my lighter 22gr (22.gr.) 500mm barrel or 26gr (.25 cal) 600mm barrel at the perfect speeds and my guns sip air. I refill because I'm getting bored and need something to do.

This is a bit off-topic but related (link).
Porting (just the end of) a barrel could be an alternative to either air strippers or a long enough barrel to allow the air behind the slug/pellet to have expanded to a lowish pressure. But, a long barrel at low fpe (with low reg pressure and/or low plenum volume and/or low valve open time) is just a waste of barrel, to use 70% or something of it's volume/length as an expansion chamber- porting might be better, if it could be done well.

 

[qball]

Those are 3 very independent subjects that are ALL important for different reasons.

BC of a pellet: higher the BC the better it resist the wind, this exponentially more important as distance increases. Obviously the 10 meter indoor crowd couldn't care less.

Speed of a pellet: not really that important until the pellet becomes destabilized by transonic turbulences, usually safe to stay under 900fps for more traditional pellets and a little higher for more slug looking pellets but staying under 900fps is always a safer bet

Barrel choice: barrel to ammo combo is most important foundational requirement or no accuracy for you!